This invention is generally directed to an apparatus and process for the preparation of toner particles, and more specifically the present invention is directed to a continuous economical process for the preparation of toner particles wherein there is effected a liquid injection into the toner components during processing thereof, enabling an increase in the viscosity of the toner polymer, in view of the lowering of the melt temperature thereby permitting a more desirable dispersing of the pigment particles therein.
In one embodiment of the present invention, there is provided a continuous process for the preparation of toner particles wherein there is injected into the polymer components selected a liquid with a boiling point below the melt temperature of the toner composition, whereby the liquid vaporizes enabling the absorption of heat generated by the shearing of the polymer melt and thereby desirably lowering the melt temperature of the toner resin particles. Liquid injection is effected in one specific embodiment with a specially designed nozzle means, however other means of injection can be used, which means are appropriately situated in a toner extrusion apparatus. This apparatus allows the continuous automatic control of toner processing parameters including the degree of dispersion of the pigment particles in the toner resin particles. With the selection of such an extrusion apparatus the properties of the toner composition can be determined during the processing thereof eliminating the need for sampling the toner subsequent to its complete preparation, which sampling is usually accomplished with each batch of toner being prepared. A suitable extrusion apparatus and process is described in a copending application U.S. Ser. No. 535,517/83 now abandoned, entitled "Apparatus and Process for Controlling Toner Properties", the disclosure of this application being totally incorporated herein by reference.
Numerous devices and processes are known for effecting the preparation of toner particles. Examples of commercially known processes include the melt blending of the toner components in a Banbury apparatus. Other methods include spray drying, dispersion polymerization, solution polymerization, and the like. Also it is known that toner compositions can be obtained with an extrusion apparatus. An extrusion apparatus and process enables a number of advantages not achievable with the Banbury process in that, for example, extrusion is a continuous rather than batch operation and, the extrusion process is more susceptible to automation, allowing more economical operation.
Moreover, it is known that water injection processes may be used for the purpose of removing undesirable volatile components during the processing of polymer compositions. However, there is no teaching in this prior art as to the concept of selecting liquid injection for the purpose of controlling, for example, the melt temperature of the polymer components needed for obtaining toner compositions, and wherein there results improved pigment dispersion. The prior art is silent with respect to processing toner compositions with a liquid injection means.
Toner compositions selected for causing the development of images in electrostatic imaging systems must be of the proper triboelectric charge in order to achieve high quality developed images of suitable resolution. The triboelectric charge is primarily effected by the degree of dispersion of the pigment particles and/or charge enchancing additives incorporated therein. Dispersion of the pigment particles and internal charging additives is directly dependent on the magnitude of the shear stress and the temperature history of the polymer components during the melt mixing processes. Accordingly in most situations a reduction in the polymer melt temperature generates higher stress enabling a more favorable dispersion therein of the pigment particles and the charge enhancing additives. However, in many of the apparatuses and processes described herein for obtaining toner particles, such as the Banbury roll mill, the compounding extruder, and the continuous mixing apparatus, the surface area required for heat transfer to reduce the melt temperature is severely limited.
Thus there remains a need for processes and apparatus for the continuous preparation of toner compositions wherein there can be effected a reduction in the melt temperature of the toner componets. Moreover, there remains a need for a simple, economical extrusion toner processing apparatus wherein the melting temperature of the polymer components can be desirably lowered by a liquid injection process. Further, there continues to be a need for enabling the liquid injection of components into the toner compositions being prepared, and wherein this injection can be effected in a continuous manner during the extrusion process. Moreover, there remains a need for a continuous process and apparatus which will enable increased dispersion of pigment particles, and/or charge enhancing additives into the toner composition components, thereby desirably effecting the resulting triboelectric charge contained on the toner resin particles. Additionally, there continues to be a need for an apparatus and process wherein liquid injection of water, suspensions with pigment particles, and charge enhancing additives, or solution mixtures having incorporated therein charge enhancing additives, can be accomplished in a continuous manner, and wherein the properties of the toner compositions produced may be continuously monitored during processing that is, on line, enabling the necessary adjustments to the equipment to be effected immediately and automatically. Furthermore, there continues to be a need for a process and apparatus which will enable a simple, economical method for continuously monitoring and maintaining the capacitance and conductance values of toner components selected for preparing the toner compositions, and wherein during toner processing there can be injected by a nozzle various components into a toner composition causing the melting temperature thereof to be desirably reduced. Also, there continues to be a need for an apparatus and process which continuously and accurately measures the capacitance, or the amount of pigment particles contained in the toner resin selected, and the conductance, that is the degree of dispersion of the pigment particles in the toner resin particles, which measurements are desirably accomplished on line enabling the automatic adjustment of various processing parameters in order that toner particles of desired properties can be obtained. Additionally, there continues to be a need for the preparation of toner particles by extrusion processes, wherein there is injected various components into the polymer resinous particles, and where toner compositions can be prepared in a continuous manner rather than in batches as is effected with the known Banbury roll mixers, which extrusion apparatus contains as an integral part thereof, a nozzle injecting means, and an optional sensing device. Moreover, there remains a need for a process and apparatus wherein there can be injected into a toner composition aqueous solutions, a suspension containing therein carbon black particles, or charge enhancing additives, a solution having dissolved therein charge enhancing additives, waxes, and the like, desirably enabling the lowering of the melt temperature of the toner composition, and causing the viscosity of the polymer contained therein to increase.